It has become common practice in the food industry to market food compositions, particularly snack food products, in a partially-finished form known as half products. The consumer must then finish preparing the product by heating it. In this final heating step, the half product is caused to expand or puff due to pressure generated by expansion of trapped moisture in the half product.
When used to produce expanded cereals, half products can be gun puffed. Such puffing cannot, however, be conducted at home by consumers due to the need for specialized equipment
Puffed snacks can also be prepared by deep fat frying the half products. However, such snack products suffer from the disadvantage of having fat levels up to 35% which elevates their caloric content and limits their shelf life.
These problems are avoided by puffing or expanding half products by microwave heating, as described in U.S. Pat. Nos. 4,251,551 ("'551 patent") and 4,409,250 ("'250 patent") both to Van Hulle et al. (collectively "the Van Hulle patents"). In the '551 patent, a cheese-coated snack product is formed, while the '250 patent is directed to a sugar-coated product. In both cases, the half product is prepared in the form of pellets which are then dispersed through or matrixed in a puffing medium which comprises an edible fatty triglyceride in the case of the cheese-flavored products and a nutritive carbohydrate sweetening agent in the case of the sugar-coated products.
When the pellets of the Van Hulle patents are subjected to microwave heating without the surrounding puffing media, not all the pellets undergo puffing. Further, localized over-heating of portions of some pellets can occur, resulting in visually unattractive products and localized charring which creates off-flavors. To avoid these problems, the pelletized half products of the Van Hulle patents are combined with the puffing media during microwave heating.
Another problem with the Van Hulle patents is that flavoring is not applied to the half product until the half product is dispersed in a puffing media containing flavoring and subjected to microwaves. Uniform coverage of flavoring over the puffed product is thus dependent upon a good distribution of half product through the puffing media. Since achievement of such a distribution is unlikely, some of the puffed half product will be heavily coated with flavoring, while some of it will not be adequately covered.
The pelletized form of the half product disclosed by the Van Hulle patents is simply configured to expand in place when subjected to microwaves. Although visualization of this phenomena has some consumer appeal, the inability of these half products to move during expansion is not particularly dynamic.